Compensated open-loop control of oxygen sensor heater

Abstract

An oxygen sensor heater control determines heater activation based on an open-loop control parameter and a correction factor that compensates for part-to-part variability. Following a cold start where the heater temperature can be reliably estimated, the engine controller predicts the resistance of the heating element and heater circuit at the desired operating temperature of the sensor, and computes the correction factor for heater activation based on the predicted resistance values and nominal resistance values. At least one predicted value is stored in non-volatile memory, and used to compute the correction factor following a warm or hot start of the engine.

1. A method of operating an exhaust gas oxygen sensor for an engine, the oxygen sensor having a electrical heating circuit including a heating element and conductor leads attached to said heating element, where a temperature of the oxygen sensor is inferred from an electrical resistance of said heating element, the method comprising the steps of:
 electrically activating said heating circuit at an activation value determined in relation to external heat transfer to said oxygen sensor; 
 determining an initial temperature of said heating circuit based on an initial cold start temperature of said engine; 
 measuring an electrical resistance of said heating circuit at said initial temperature; 
 predicting hot operational electrical resistances of said heating element and said heating circuit based on said measured resistance, assumed hot operational temperatures of said heating element and said conductor leads, and a nominal resistance of said conductor leads; and 
 modifying said activation value based on said predicted hot operational electrical resistances, the nominal resistance of said conductor leads, the nominal resistance of said conductor leads, and a nominal resistance of said heater circuit so as to compensate for oxygen sensor variations. 
 
   
   
     2. The method of  claim 1 , including the steps of:
 storing a computed parameter used to modify said activation value; and thereafter 
 using the stored parameter to modify said activation value. 
 
   
   
     3. The method of  claim 2 , including the steps of:
 repeating the method following a subsequent cold start of said engine to re-predict the hot operational electrical resistances of said heating element and said heating circuit; and 
 updating said stored parameter based on the re-predicted hot operational electrical resistances. 
 
   
   
     4. The method of  claim 1 , where the nominal resistance of said conductor leads is specified for a base temperature, and the method includes the steps of:
 determining a nominal resistance of said conductor leads for said initial temperature based on the specified nominal resistance of said conductor leads, said base temperature and said initial temperature; 
 determining a resistance of said heating element for said initial temperature according to a difference between the measured resistance of said heating circuit and said nominal resistance of said conductor leads for said initial temperature; and 
 predicting the hot operational resistance of said heating element based on said resistance of said heating element for said initial temperature and the assumed hot operational temperature of said heating element. 
 
   
   
     5. The method of  claim 4 , including the steps of:
 determining a nominal resistance of said conductor leads for said hot operational temperature of said conductor leads based on the specified nominal resistance of said conductor leads, said base temperature and said hot operational temperature of said conductor leads; and 
 predicting the hot operational resistance of said heating circuit according to a sum of the predicted hot operational resistance of said heating element and said nominal resistance of said conductor leads for said hot operational temperature of said conductor leads. 
 
   
   
     6. The method of  claim 1 , including the steps of:
 computing a correction factor for said activation value that will compensate said activation value for said oxygen sensor variations, based on said predicted hot operational electrical resistances, a nominal resistance of said heating element at said hot operational temperature of said heating element, and a nominal hot operational resistance of said heater circuit; and 
 modifying said activation value by applying said correction factor to said activation value, and activating said heating element at the modified activation value. 
 
   
   
     7. The method of  claim 6 , where the nominal resistances of said heater circuit and said conductor leads are specified for a base temperature, and the method includes the steps of:
 determining a nominal resistance of said heating element for said base temperature according to a difference between the specified nominal resistances of said heating circuit and said conductor leads; 
 determining the nominal resistance of said heating element for said hot operational temperature of said heating element based on said nominal resistance of said heating element for said base temperature, said base temperature, and said hot operational temperature of said heating element. 
 
   
   
     8. The method of  claim 7 , including the steps of:
 determining a nominal resistance of said conductor leads for said hot operational temperature of said conductor leads based on the specified nominal resistance of said conductor leads, said base temperature and said hot operational temperature of said conductor leads; and 
 determining a nominal hot operational resistance of said heater circuit according to a sum of said nominal resistance of said heating element for said hot operational temperature of said heating element and said nominal resistance of said conductor leads for said hot operational temperature of said conductor leads.